There has been known a conventional method of forming a cam shaft, in which, after a preliminary shaft is inserted into a cam-lobe shaft hole of a cam lobe, the preliminary shaft having a diameter smaller than that of the cam-lobe shaft hole, a side projecting part is formed on an outer circumference of the preliminary shaft positioned near a side surface of the cam lobe, the side projecting part having a diameter larger than that of the cam-lobe shaft hole, so that the cam lobe and the preliminary shaft are assembled to each other (FR-2630790-A).
There has been known another method of forming a cam shaft, in which a shaft-hole projecting part is previously formed on an area, which is to be opposed to the inner surface of a cam-lobe shaft hole (an area corresponding to an axial length of the cam-lobe shaft hole), of the outer circumference of a preliminary shaft, the shaft-hole projecting part having a diameter larger than that of the cam-lobe shaft hole, and the shaft-hole projecting part is press-inserted into the cam-lobe shaft hole, so that the cam lobe and the preliminary shaft are assembled to each other (see, JP9-96202A).
There has been known still another method of forming a cam shaft, in which a cam lobe is heated so as to increase a diameter of a cam-lobe shaft hole by thermal expansion, a preliminary shaft, which has a diameter smaller than that of the cam-lobe shaft hole which has been increased, is inserted into the cam-lobe shaft hole whose diameter has been increased, and then the cam lobe is cooled so as to decrease the diameter of the cam-robe shaft hole, so that the cam lobe and the preliminary shaft are assembled to each other JP4-334706A).